The present invention relates to a process for converting a high-boiling hydrocarbon feedstock into lighter boiling hydrocarbon products. More in detail, the present invention relates to a process for converting hydrocarbons, especially hydrocarbons originating from refinery operations, such as for example atmospheric distillation unit or a fluid catalytic cracking unit (FCC), into lighter boiling hydrocracked hydrocarbons having a boiling point lower than naphthalene and lower.
U.S. Pat. No. 4,137,147 relates to a process for manufacturing ethylene and propylene from a charge having a distillation point lower than about 360 DEG C. and containing at least normal and iso-paraffins having at least 4 carbon atoms per molecule, wherein: the charge is subjected to a hydrogenolysis reaction in a hydrogenolysis zone, in the presence of a catalyst, (b) the effluents from the hydrogenolysis reaction are fed to a separation zone from which are discharged (i) from the top, methane and possibly hydrogen, (ii) a fraction consisting essentially of hydrocarbons with 2 and 3 carbon atoms per molecule, and (iii) from the bottom, a fraction consisting essentially of hydrocarbons with at least 4 carbon atoms per molecule, (c) only the fraction consisting essentially of hydrocarbons with 2 and 3 carbon atoms per molecule is fed to a steam-cracking zone, in the presence of steam, to transform at least a portion of the hydrocarbons with 2 and 3 carbon atoms per molecule to monoolefinic hydrocarbons; the fraction consisting essentially of hydrocarbons with at least 4 carbon atoms per molecule, obtained from the bottom of the separation zone, is supplied to a second hydrogenolysis zone where it is treated in the presence of a catalyst, the effluent from the second hydrogenolysis zone is supplied to a separation zone to discharge, on the one hand, hydrocarbons with at least 4 carbon atoms per molecule which are recycled at least partly to the second hydrogenolysis zone, and, on the other hand, a fraction consisting essentially of a mixture of hydrogen, methane and saturated hydrocarbons with 2 and 3 carbon atoms per molecule; a hydrogen stream and a methane stream are separated from the mixture and there is fed to the steam-cracking zone the hydrocarbons of the mixture with 2 and 3 carbon atoms, together with the fraction consisting essentially of hydrocarbons with 2 and 3 carbon atoms per molecule as recovered from the separation zone following the first hydrogenolysis zone. At the outlet of the steam-cracking zone are thus obtained, in addition to a stream of methane and hydrogen and a stream of paraffinic hydrocarbons with 2 and 3 carbon atoms per molecule, olefins with 2 and 3 carbon atoms per molecule and products with at least 4 carbon atoms per molecule.
U.S. Pat. No. 3,317,419 relates to a process for hydrorefining a hydrocarbon charge stock comprising hydrocarbons boiling above the gasoline boiling range which process comprises the steps of: (a) hydrocracking and hydrorefining said charge stock in admixture with hydrogen in a first reaction zone containing a hydrorefining catalytic composite; (b) separating the normally liquid product effluent from said first reaction zone into a first light fraction and a heavier fraction; (c) combining at least a portion of said first light fraction with a hydrocarbon mixture and reacting the resulting mixture with hydrogen at a temperature within said range in a second reaction zone containing a hydrorefining catalytic composite and maintained under less severe conversion conditions than said first zone; (d) separating the normally liquid product effluent from said second reaction zone into a second light fraction and a hydrorefined second heavy fraction; (e) combining at least a portion of said second light fraction with a hydrocarbon mixture, reacting the resulting mixture with hydrogen in a third reaction zone containing a hydrorefining catalytic composite and maintained under conditions to effect hydrogenative hydrorefining of said mixture within minimum hydrocracking; and,(f) separating the product effluent from said third reaction zone into a normally gaseous phase and a hydrorefined third heavy fraction.
GB 1,161,725 relates to process for selectively producing gasoline boiling range hydrocarbons by hydrocracking which comprises, contacting under hydrocracking conditions a heavy petroleum hydrocarbon feed with an amorphous base hydrocracking catalyst and a zeolite base hydrocracking catalyst, said contact being carried out in a series of catalyst beds wherein said amorphous base catalyst is separated from said zeolite base catalyst, recovering a normally liquid effluent from the last catalyst bed, separating a gasoline boiling range fraction from said liquid effluent, and recycling at least a portion of the liquid effluent boiling above the gasoline range to contact the amorphous base hydrocracking catalyst bed. The conditions in the first hydrocracking stage are maintained at a temperature in the range of between 550 F and 750 F and a total pressure in the range of between 1000 psig and 3000 psig, whereas the conditions in the second hydrocracking stage are similar, i.e. maintained at a temperature of between 550 F. and 750 F., and a total pressure of between 1000 psig and 2000 psig.
U.S. Pat. No. 3,360,456 relates to a process for the hydrocracking of hydrocarbons in two stages to produce gasoline with a reduced consumption of hydrogen wherein the temperature conditions in the first hydrocracking stage are higher than the temperature conditions in the second hydrocracking stage.
GB 1,020,595 relates to a process for the production of naphthalene and benzene which comprises passing a feedstock, containing alkyl-substituted aromatic hydrocarbons boiling within the range 200-600 F and comprising both alkyl benzenes and alkyl naphthalenes into a first hydrocracker at a temperature from 800 to 1100 F, a pressure from 150 to 1000 psig, or in the absence of a catalyst at a temperature from 1000 to 1100 F, a pressure from 150 to 1000 psig, subjecting the cracked product to hydrocracking in a second hydrocracker either in the presence of a catalyst at a temperature from 900 to 1200 F, a pressure from 150 to 1000 psig or in the absence of a catalyst at a temperature from 1100 to 1800 F and a pressure from 50 to 2500 psig.
U.S. Pat. No. 3,660,270 relates to a process for producing gasoline which comprises hydrocracking a petroleum distillate in a first conversion zone, separating the effluent from the first conversion zone into a light naphtha fraction, a second fraction having an initial boiling point between 180 and 280 F, and an end boiling point between about 500 to 600 F., and a third heavy fraction, hydrocracking and dehydrogenating the second fraction in a second conversion zone in the presence of a catalyst and recovering from the second conversion zone at least one naphtha product.
US patent application No 2007/112237 relates to a method of preparing aromatic hydrocarbons and liquefied petroleum gas (LPG) from a hydrocarbon mixture, comprising the following steps of: (a) introducing a hydrocarbon feedstock mixture and hydrogen into at least one reaction zone; (b) converting the hydrocarbon feedstock mixture in the presence of a catalyst to (i) a non-aromatic hydrocarbon compound which is abundant in LPG through hydrocracking and to (ii) an aromatic hydrocarbon compound which is abundant in benzene, toluene and xylene (BTX) through dealkylation/transalkylation within the reaction zone; and (c) recovering the LPG and aromatic hydrocarbon compound, respectively from the reaction products of step (b) through gas-liquid separation and distillation.
WO2008/043066 relates to a process for producing one or more middle distillate fuels, including (a) dehydrogenating/aromatizing a paraffinic naphtha stream into a composition containing olefins and aromatic hydrocarbons (b) subjecting the olefins and aromatic components to aromatic alkylation, and (c) separating the alkyl aromatics of middle distillate range.
U.S. Pat. No. 5,603,824 relates to an integrated hydroprocessing method in which hydrocracking, dewaxing and desulfurization all occur in a single, vertical two bed reactor, wherein a distillate is split into heavy and light fractions, the heavy fraction being hydrocracked and partially desulfurized in the top reactor bed, and the effluent from the top bed is then combined with the light fraction and is cascaded into the bottom reactor bed, where dewaxing for pour point reduction and further desulfurization occurs.
US patent application No 2003/221990 relates to a process for the production of light products, such as gas and naphtha, by processing kerosene in a second stage of a multi-stage hydrocracker, wherein kerosene, diesel and naphtha from other sources are included in the recycle, and subsequent hydroprocessing stages are maintained at lower pressures than the initial hydroprocessing stage.
Conventionally, crude oil is processed, via distillation, into a number of cuts such as naphtha, gas oils and residua. Each of these cuts has a number of potential uses such as for producing transportation fuels such as gasoline, diesel and kerosene or as feeds to some petrochemicals and other processing units.
Light crude oil cuts such a naphtha's and some gas oils can be used for producing light olefins and single ring aromatic compounds via processes such as steam cracking in which the hydrocarbon feed stream is evaporated and diluted with steam then exposed to a very high temperature (800° C. to 860° C.) in short residence time (<1 second) furnace (reactor) tubes. In such a process the hydrocarbon molecules in the feed are transformed into (on average) shorter molecules and molecules with lower hydrogen to carbon ratios (such as olefins) when compared to the feed molecules. This process also generates hydrogen as a useful by-product and significant quantities of lower value co-products such as methane and C9+ Aromatics and condensed aromatic species (containing two or more aromatic rings which share edges).
Typically, the heavier (or higher boiling point) aromatic rich streams, such as residua are further processed in a crude oil refinery to maximize the yields of lighter (distillable) products from the crude oil. This processing can be carried out by processes such as hydro-cracking (whereby the hydro-cracker feed is exposed to a suitable catalyst under conditions which result in some fraction of the feed molecules being broken into shorter hydrocarbon molecules with the simultaneous addition of hydrogen). Heavy refinery stream hydrocracking is typically carried out at high pressures and temperatures and thus has a high capital cost.
An aspect of such a combination of crude oil distillation and steam cracking of the lighter distillation cuts is the capital and other costs associated with the fractional distillation of crude oil. Heavier crude oil cuts (i.e. those boiling beyond ˜350° C.) are relatively rich in substituted aromatic species and especially substituted condensed aromatic species (containing two or more aromatic rings which share edges) and under steam cracking conditions these materials yield substantial quantities of heavy by products such as C9+ aromatics and condensed aromatics. Hence, a consequence of the conventional combination of crude oil distillation and steam cracking is that a substantial fraction of the crude oil, for example 50% by weight, is not processed via the steam cracker as the cracking yield of valuable products from heavier cuts is not considered to be sufficiently high.
Another aspect of the conventional hydrocracking of heavy refinery streams such as residua is that this is typically carried out under compromise conditions which are chosen to achieve the desired overall conversion. As the feed streams contain a mixture of species with a range of easiness of cracking this results in some fraction of the distillable products formed by hydrocracking of relatively easily hydrocracked species being further converted under the conditions necessary to hydrocrack species more difficult to hydrocrack. This increases the hydrogen consumption and heat management difficulties associated with the process. This also increases the yield of light molecules such as methane at the expense of more valuable species.
US patent application No's 2012/0125813, US 2012/0125812 and US 2012/0125811 relate to a process for cracking a heavy hydrocarbon feed comprising a vaporization step, a distillation step, a coking step, a hydroprocessing step, and a steam cracking step. For example, US patent application No 2012/0125813 relates to a process for steam cracking a heavy hydrocarbon feed to produce ethylene, propylene, C4 olefins, pyrolysis gasoline, and other products, wherein steam cracking of hydrocarbons, i.e. a mixture of a hydrocarbon feed such as ethane, propane, naphtha, gas oil, or other hydrocarbon fractions, is a non-catalytic petrochemical process that is widely used to produce olefins such as ethylene, propylene, butenes, butadiene, and aromatics such as benzene, toluene, and xylenes.
US patent application No 2009/0050523 relates to the formation of olefins by thermal cracking in a pyrolysis furnace of liquid whole crude oil and/or condensate derived from natural gas in a manner that is integrated with a hydrocracking operation.
US patent application No 2008/0093261 relates to the formation of olefins by hydrocarbon thermal cracking in a pyrolysis furnace of liquid whole crude oil and/or condensate derived from natural gas in a manner that is integrated with a crude oil refinery.